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THE DEVELOPMENT OF THE RELEASING FACTOR CONCEPT
Author(s) -
FINK G.
Publication year - 1976
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1111/j.1365-2265.1976.tb03833.x
Subject(s) - medicine , endocrinology , hormone , thyrotropic cell , gonadotropic cell , secretion , luteinizing hormone , hypothalamus , gonadotropin releasing hormone , peptide hormone , biology
?summary Ater four decades of intense and competitive research, three hypothalamic releasing hormones (formerly factors) hav recently been isolated and characterized. These are the decapeptide gonadotrophin releasing hormone (GnRH), tripeptide thyrotorphin releasing hormone (TRH), and the teradecapeptide somatotain. Some aspects of these hormones are discussed, and CnRH is considered in greater details to demonstrate the difficulties involved in fulfilling completely the criteria which edtermine whether a substance can be accepted as a physiologica releasing hormone. A substance immunologically similar to GnRH is present in rat phypophysial portal vessel blood, but, while the amount of this substance released into the portal circulation can be increased significantyly by electrical stim;ulation of the preoptic area, no significant ch;anges occur during the oestrous cycle or after long‐term castration. This may be due to interference with the normal secretion of GnRH by the trauma and anaesthesia which necessarilyl accompany exposure of the pituitray stalk. However, the possibility exists that our preonceived jnotions regarding the changes in plasma levels of releasing hormones under physiological conditions may be incorrect. Thus it seems likely that changes in the rate of secretion of thyrotrophin is effected by thyroid hormones modulating the responsiveness of the thyrotrophs to steady input of TRH. Evidence is presented for the existence of a similar mechanism for gonadotrophin secretion, and the role of steroid hormones and the priming effect of GnRh in modulating the responsiveness of the gonadotrophs is considered. The interinsic connexions of the hypothalamu;s, the role of the hypothalamic aminergic systems and the autonomy of the hypothalamus with repect to anterior pituitary contro present many problems which will prove difficult to solve.